Electron discharge device



1933- c. M. SLACK ELECTRON DISCHARGE DEVICE Filed July 31', 1928 r1: Flunlnvnuaio K R 6 m 0 w if m A C Y B Patented Aug. 1, 1933 1,920,601 ELECTRON DISCHARGE DEVICE Charles Morse Slack, Bloomfield,

N. J., assignor to Westinghouse Lamp Company, a Corporation of Pennsylvania Application July 31, 1928. Serial No. 296,489 11 Claims. (Cl. 250-35) This invention relates to an electron discharge device for and method of producing high electron velocities and to the application or such high speed electrons for the production of X-radiations of high frequency and, consequently,-high penetrating power, or for producing a stream of high velocity cathode or Lenard rays for germicidal and other purposes.

In the operation of X-ray tubes, either of the gaseous or high vacuum type, the penetrating power of the rays depends upon the frequency of the X-radiation, which in turn depends upon the velocity of the electrons by which they are produced. It .is necessa in many instances, in

order to produce X-radiation of sufflcient penetration for radiography and therapeutic purposes, to employ a potential difference between the electrodes of several in order to create electron velocities of sumcient magnitude to generate X-radiation of the desired high frequency.

' Also, in the production of cathode ray tubes of the type in which the electrons are projected at high velocities through a wall of the tube into the 3 open air so as to be available for various purposes, such as eiiecting chemical reactions or for germicidal and sterilizing effects, or for the pro-' duction of oscillograms, it is necessary to impress between the electrodes extremely high voltages to 0 create suiiicient electron velocities to penetrate the wall of the tube and into the outer atmosphere the required distances. Cathode ray, tubes of this type have'been constructed for operation with a potential drop therethrough of several hundred 5 thousand vol The frequency of the X-rays and the electron velocity available for the cathode ray tubes, are restricted by the available voltages which may be impressed upon the electrodes. The voltages 3 which are now available for use in the operation of such devices are limited by practical considerations and cannot be readily increased due to increased insulating difliculties in the tubes.

It is an'object of the present invention, there- F fore, to provide a method of and device for obtaining electron velocities of a much greater magnitude than have been obtainable heretofore by the direct application of a voltage of a definite value between the electrodes.

A further object is to provide a method of and a tube for producing X-radiation of higher frequency than those obtainable directly by the voltage applied between the electrodes.

Other objects will appear hereinafter.

My invention is based upon the phenomenon hundred thousand volts,

that when X-rays fall upon a substance, electrons are ejected therefrom with an initial velocity of the same order as the velocity of the electrons producing the X-ray. The velocity of these sec-' ondary electrons is then increased by causing them to fall through a difference of potential which may be the same as that which produced the X-rays, by which such secondary electrons were generated. The high velocity secondary electrons may then be employed for producing other X-rays of higher frequency, or may be utilized as a source of cathode rays for projection through the walls of the device.

The invention will be more fully understood by reference to the accompanying drawing, in which:

Figure 1 is a sectional view of an X-ray tube embodying my invention;

Figure 2 is a sectional view of a modified form of tube; and t Figure 3 is a sectional view of a cathode ray tube embodying the principle of my'invention.

The device shown in Figure 1 comprises a glass envelope 1 containing a filamentary cathode 2 and an anti-cathode or target 3. The cathode end 4 of the tube has a reentrant glass stem 5 terminating in a press 6 through which the leading-in conductors '7 for the cathode are sealed. The cathode 2 may be of any suitable electron emit ting material, but I prefer to construct it of tungsten or tantalum in the form of a coil mounted within a focusing cup 8, as is usual in X-ray construction.

An electrostatic shield 9 surrounds the cathode and protects the seal from puncturing. It also prevents sharp point sparking'from the cathode. This shield may take the form of a split metal tube of nickel, monel metal chrome-iron or other metal, held in place on friction. Obviously, other convenient methods of support maybe employed.

The anti-cathode or target 3 may consist of a solid cylindrical metal block 10, preferably-of copper, with an inclined face 11 containing a rei'ractory metal insert or disc 12 of a metal of high atomic weight, such as tungsten. The anti-cathode is supported on a metal tube 13 carried by the reentrant stem 14 and current is conducted thereto by a leading-in conductor 15 sealed through the press. v

A second cathode 16 is positioned adjacent the cathode 2 and is electrically connected thereto. This cathode is made the electrons generated therein upon a secondary target 17 which may form a part of the anticathode 3. The secondary target is provided'with' the, reentrant stem 5 by concave in order to focus.-

a refractory face 18 upon which the secondary electrons impinge.

A high potential, such as ordinarily employed in x-ray tube operation, may be impressed between the cathodes 2 and 16 and the anti-cathodes 3 and 17 and a heating current may be passed through the cathode 2 to heat the same to an electron emitting temperature. With such an arra'ngement, electrons emitted thermally by the cathode 2 will be drawn over to the anti-cathode 3 by the potential difference between these electrodes and will generate X-rays from the face 12 of the anti-cathode.

The primary electrons emitted by the incandescent cathode 2 at a low initial velocity, in traversing the space between the cathode and the anti-cathode 3, attain a velocity dependent upon the magnitude of the voltage diiference between the electrodes. The final velocity of the electrons, at point of impact with the target 12 may be determined by the equation.

Ve= mv =hy in which '7 represents the frequency of the X-radi- 35 ations, m the mass of the electron, equal to about 9 x 10- gms., and h is Plancks constant, which a is equal to about 6.55 x 10- ergs sec.

The X-rays developed at the target 12,are proiected in all directions from the face thereof and 40 consist largely 'of rays near the limiting frequency, as determined by the velocity of the impinging electron. Some of these X-rays are directed against the concave face of the secondary cathode 16 and give rise to secondary electrons. The initial velocity of these secondary,

electrons is dependent upon the frequency of the X-rays producing them and is equalto the velocity of the electrons which originally produced the X-rays. The initial velocity of the secondary electrons may be expressed bythe same equation, which expresses the relationship between the velocity of the primary electron and the frequency of the resultant X-ray,namely trons from the cathode 2. The maximum or limiting velocity which any of these secondary electrons can have at point of impact upon the target 18, will be twice that attained by the highest velocity primary electrons at point of impact with '75 the anti-cathode 11"br. twice thflt obtainable diat potentials of 100,000 volts applied directly berectly by the potential difierence between the electrodes.

It will be appreciated, of course, that the number of secondary electrons of high velocity will be much lower than the number of primary electrons, since only a small portion of the X-rays strike the secondary cathode 16.

The secondary electrons upon impact with the 7 target 18 generate X-rays of a frequency very much higher than the rays generated by the primary electrons and, consequently, higher than can be obtained directly by the voltage difference between the electrodes. These X-rays of higher frequency have greater penetrating power.

The reference characters A, B, C and D indicate, respectively, the possible path of a primary electron, the resultant X-radiation, the secondary electron generated thereby, and the final X-radiation. g v

In Figure 2 is shown a modification which is designed to give greater eliiciency due to increased area of the secondary cathode upon which the original X-rays may strike. In this modification the secondary cathode 20 is disposed about the primary cathode, and a single o anti-cathode 21 is provided for both the primary and secondary electrons. It will be'understood that in the device of both Figures 1 and 2, the X-rays generated by the secondary electrons, which for convenience may be termed the secondary X-rays, may produce tertiary electrons which in turn may produce tertiary X-rays and this may be repeated a number of times, each cycle producing electrons of increased initial velocity, but in very much smallernumbers.

In Figure 3 I have shown a cathode ray tube comprising the envelope 22 having a cathode 23 similar to that shown in Figure 1, a second and a third cathode 24 and 25, and a target or anticathode 26. 5

The electrons emitted at high velocity from the cathode 25 are focused through a tubular anode 27 mounted in a tubular extension 28 of the envelope. The anode 27 is provided with a terminal 29 which may be connected to the same source of potential as the anti-cathode 26. The anode 2'1 serves to project the electron stream at high velocity through a thin glass window 30 blown in the end of the tubular extension 28. The construction of this window and the arrangement of the anode relative thereto is more fully described in my copending application Serial No. 272,194, filed April 23, 1928, and entitled Cathode ray tube.

The window 30 may have a dome thickness of from .0001 to .005 inches and is permeable to high velocity electrons with only a small loss of energy. Thus, with a window having a thickness of .001 inches the energy absorption in the glass tween the anode and an incandescent cathode, without the intervention of the intermediate electrodes 24, 25 and 26, corresponds to a decrease in inter-electrode potential of only about 16,000 volts, and at 200,000 volts there is a loss .of energy corresponding only to .a decrease of about 8,000 volts between the electrodes. Since the energy loss in the glass decreases as the velocity of the electron stream increases. with the very high speed electrons obtained by the generation of cathode rays by high frequency X- rays, a much smaller energy loss is suffered in the window of the cathode ray tube from that obtainable by the direct application of the same inter-electrode voltage and due to the increased 151 envelope containing an electron enclosing envelope,

velocity of the electrons projected through the window greater penetrability in the open air is obtained.

Obviously other applications of the high velocity cathode stream may be devised and the apparatus for producing such high velocity electrons and high limiting frequency -X-radiations may be devised without departing from the invention andI do not desire to be limited to the particular embodiments shown and described.

What is claimed is: Y

1. An electron discharge device comprising an emitting cathode, an anode disposed opposite said cathode, means for directing the electrons from said cathode upon said anode to produce X-radiations,

a second cathodepositioned to intercept a portion of said X-radiations and to produce secondary electron emission therefroin, and means for increasing the velocity. of said secondary electrons.

2. An electron discharge device comprising an enclosing envelope, a source of primary electrons of low initial velocity, means for accelerating said electrons to a high 'X-radiations therefrom, means for generating secondary-electrons of high initial velocity by said x-radiations, and means for increasing the velocity of said secondary electrons.

3. An electron discharge device comprising an a source of initial velocity dependent upon the frequency of said X-radlations, and means for increasing the velocity of said electrons. 1

4. An electron discharge device comprising an a source of x-radiations, means for generating electrons ,with said xradiations having an initial velocity dependent on the frequency of said x-radiations, and an electrode serving as an anode for said cathode for increasing the velocity of said electrons.

5. An-clectron discharge device comprising an enclosing envelope, a'source of x-radiations, a cathode positioned to intercept said X-radiations and to generate electrons having a high initial velocity, and means for increasing the velocity of said electrons.

6. An electron discharge device comprising an enclosing-envelope, a source of X-radiations, a cathode positioned to intercept said X-radiations and to generate electrons having a high initial velocity, and means for increasing the velocity of said electrons and producing X-radiations of higher limiting frequency than the limiting frequency of said source of X-radiations.

. de, an anti-cathode,

velocity and producingthe second cathode and said anode.

7. An electron discharge device comprising an enclosing envelope, a thermionically active cathmeans for directing a stream of electrons from said cathode upon said anticathode for producing X-radiations, a second cathode electrically connected to said thermionically active cathode and positioned to intercept a portion of said X-radiations and to produce secondary electrons, and means for generating other X-radiations with said secondary electrons.

8. An X-ray tube for producing X-radiations of high frequency comprising an enclosing envelope, a cathode, an anti-cathode cooperating therewith to produce X-radiations under the infiuence of an impressed potential, a second cathode disposed adjacent said first mentioned cathode to intercept said X-radiations and to produce secondary electrons having a high initial velocity, said second cathode forming means for directing said secondary electrons upon said anti-cathode to generate additional X-radiations.

9. The method of producing X-rays of high frequency comprising generating X-rays of lower frequency, utilizing said cathode rays having a maximum. initial velocity dependent on the limiting frequency of said X-rays, increasing the velocity of said cathode rays and utilizing said high velocity electrons to produce X-rays of high frequency.

10. An electron discharge device comprising an enclosing envelo a source of electrons, an anode, means for focusing said electrons upon X-rays to produce said anode and producing x-radiations at said anode under the influence of a potential difference between the electrodes, a second cathode positioned so as to intercept a portion of said X- generate secondary electrons tube comprising an enclosing a cathode, an anti-cathode cooperating for producing X-radiations under the of an impressed potential, a second v concave shape disposed adjacent said first mentioned cathode and electrically connected thereto for intercepting said X-radiations, producing secondary electrons having an initial velocity dependent upon the frequency of said x radiations and directing said secondary electrons onto said anti-cathode to generate addi- 11. An X-ray envelope, therewith tional X-radiations of higher limiting frequency than said first generated X-radiations.

CHARLES MORSE SLACK. 

